Wow. Way to give an interesting title. It really grasp people's attention.
So I had a brainfart two days ago about Tokyo Ghoul and I was like "I could write about this". So her I am.
A little exposition: I saw the first and second season of the anime (even thou I barely remember anything about that garbage second season) and I read the manga for a while. About as far as the second season go.
For those who don't know anything about the show Tokyo Ghoul is a story where besides humans there are creatures called ghouls (no shit really?) whom look like humans and also eat humans. They have supernatural strenght and regeneration, they can't be injured via normal weapons and have a special organ somewhere on their backs (depends on the type of the ghoul... there are four types) from which a weapon-like body-part can come out called kagune. They are only able to eat human flesh, they need to consume a whole human every week to survive and they get sick from human food. And that's pretty much everything without spoilers. Most of this knowledge are told in the first episode.
From here on out: MAJOR SPOILERS!!!
So according to what we know after watching the anime (both seasons) or reading the manga that far we are told that noone knows anything about the evolutional predecessors of the ghouls BUT! We know they look exactly the same and they are able to reproduce with each other (under some... complicated circumstances) and also it is possible for a human to receive ghoul organs during a surgery and survive with the side-effect of turning into a ghoul (more or less). We don't know if it can work backwards or not but I would say I'm a hundred percent sure that the answer is maybe.
To understand my theory we have to put on our conspiracy hats and go back in time when mankind ascended from mere animals into the glorius species that it is today (I hope you feel the sarcasm here) and take a little detour into biology, evolution and parasytes.
So let's start with the parasyte part. Parasytes are creatures whom lives on/in other creatures wheter it is a plant or an animal. There are many types of them. There are some that are just clinge onto the host and lives there happily ever after. There are some that are trying to take over the hosts body. There are some that just straight-up kills the host. And there are some that lives in a symbiosis (btw english isn't my primal language, so forgive me if I misspell some words).
They can do quite a lot, in fact they can be an influence to the evolution of a species.
Conspiracy time! So we are in the past somewhere before mankind stood up permanently but after it became clear that they will be something else then the other species. They are clearly becoming a threat to the other species in terms of dominance. It starts effecting the environments wildlife etc. So the food-chain is being redrawn and everything starts to reallocate itself. You know, trying to find a way to survive. And a type of parasyte in particular makes it's way to a pre-human (...pre-human... sounds weird). This parasyte has the ability to manipulate the brain boosting phisycal abillities strenghtening the host thus their own survival method. They partially capable of taking over the host giving them intense killer intent for example to hunt down a prey. Now as evolution goes on and on the parasyte following the same method that every hunting creature followed since they exist, "the easier the prey, the better it is) they start forcing the host to go on a killing rampage whent their own kind is around (the ones that are not infected with the parasyte). As humans developed a kind of hierarchy amongst themeselves, they decide to abandon the infected individuals. Of course it doesn't go as planned. The infected fights back and since they are stronger, humans using their brains make weapons and fight them off. The infected during the years of hunting humans develop "differences". Claws or fangs things like that. But humans are clever they try to close out the not-so-anymore-humans. Of course the infected tries to get rid of these tiny ass parasytes inside of their bodies but they can't. But the parasyte as a safety plan changes the hosts organs in a way that they can only eat human flesh. So with starvation on the horizon a new way must be found to get the easy prey.
Timeout.
Here comes the biology part. So the human body is capable of so many thing that it's almost impossible to list everything. But it can save nutrients (again, not sure if I spelled that right) in the bodycells and use it in emergency. For example to heal the body itself. A little genetical twist and they stack up way more so the body is able to heal faster to the point of super regeneration.
Timeout over.
So they develop this spuer regen and with that they get something way more dangerous. To duplicate the bodycells so fast they can grow claws, fangs etc. in mere seconds. Sneak into the humans place then attack. But it's useless because once they grew claws they can't get rid off them.
And here comes the real kicker. They develop an organ filled with the parasytes and bodycells containing a shitton of saved energy from previous feasts. Using that organ they can grow out "something" to kill the prey and when they are done the parasytes basically eat up the cells so it won't go to waste and most importantly they can hide again. Of course there are side-effects.
-need to eat a whole human every week
-when starving the hunger takes over the mind sending the host on a rampage
-as the quick-paced evolution kicked in there were things they couldn't get rid off
-their eyes turning black/red to paralyze the prey in fear for example
Now a little bit about the organ called kagune. There are four types each specialised in something, speed for example. The reason behind that is in the past. By the time ghouls reached the level where they had kagune (around the middle-age, a bit before that) there were different types of societys out there. Nomads, villages, cities, kingdoms. different preys requierd different hunting methods. Chasing after nomads on horses, or fighting back against armored knights etc.
After checking what I wrote so far it became quite clear that this theory is an asspull. There are a couple of things I'd still want to talk about but it's 04:45 in the AM here and I haven't slept for 40 hours straight so I'm gonna write about hose things later. How Kanekis ghoulification works and why is the One-Eyed Owl is bullshit because given by the time that passed both of his eyes should have turned black/red. The same goes for Kaneki.
Anyway it was fun. Hope you enyojed it. Upvote if you would like to read some more and we will meet in my next asspull.
And remember, that's just a theory. An Anime Theory. (<- haha get it?)